It is well known to provide an oil supply system for an engine that supplies oil from a reservoir, often referred to as a sump, to various components on the engine requiring a supply of oil, such as bearings, pistons, hydraulic valve mechanisms, and piston cooling jets.
However, the inventors herein have identified a number of issues with the above approach. The flow of oil is not based upon the operating state of the engine, and so at times a high flow of oil is provided when in fact a lower flow of oil would be adequate, causing an oversupply of oil that uses unnecessary power, and so has a negative effect on fuel economy.
It is a particular problem in respect to the use of piston cooling jets that if oil is supplied to the pistons to cool them when the engine is operating at low load, overcooling of the pistons can take place, which has an adverse effect on fuel economy as well as requiring the circulation of a greater volume of oil than would otherwise be necessary to meet the lubrication needs of the engine, thereby further reducing fuel economy.
Accordingly, systems and methods are disclosed herein to at least partially address the above issues. One embodiment includes a method for controlling oil flow in an engine. The method comprises adjusting oil pressure inversely with engine speed by adjusting a solenoid valve hydraulically coupled with an oil pump, and selectively routing oil through an oil galley to a piston cooling jet via a pressure-operated valve responsive to the adjusted oil pressure. Responsive to identified degradation of the solenoid valve, the pressure may be increased irrespective of engine speed to supply oil cooling jet operation.
Another embodiment includes an oil supply system for a reciprocating piston internal combustion engine, the system comprising an electronic control unit, an oil reservoir, a pump to supply oil at pressure from the reservoir to components including at least one piston cooling jet requiring a supply of oil, and at least one pressure-operated valve to supply oil to the at least one piston cooling jet, each pressure-operated valve coupled to one piston cooling jet and configured to open at a predefined valve opening pressure. Each piston cooling jet may be supplied with oil through a pressure operated valve, and the pump may be operable to supply oil in a low pressure mode of operation at a first predefined pressure below the predefined valve opening pressure and to supply oil in a high pressure mode at a second predefined pressure above the predefined valve opening pressure. The electronic control unit is operable to select the operating mode of the pump based upon a predefined relationship between engine speed and engine load.
The piston cooling jets may be supplied with oil when oil pressure is above a threshold. The oil pressure may be determined by a combination of engine speed and load such that during certain operating conditions, the piston jets receive oil that is in turn supplied to the pistons of the engine to provide cooling, while during other operating conditions, the piston jets do not receive oil and thus the pistons are not cooled. In this manner, the oil supply system is operable to match oil supply to the operating conditions of the engine so as to reduce fuel usage. Further, the pressure output by the oil pump may be adjusted by adjusting a solenoid valve coupled to the pump. The oil pump and solenoid valve are configured to output high pressure oil in response to a degradation of the solenoid valve, such that the pistons may be cooled even if a failure in the solenoid valve occurs.